PRACTICAL ORGANIC CHEMISTRY 3. Orthoformic ester and acetoacetic ester in presence of acetic anhydride form a hydroxymethylene ester (Claisen), CH, CH3 I " I CO CO Clio + HC(OOCJLj)8 = C:CH.OCol-L; + 2CoH->OH, I - " | COOC2II5 COOCjIIg 4. The derivatives of acetosuccinic ester are very numerous the compound lending itself readily to the formation of hetero- cydic compounds (pyrrole, furfurane, thiophene, pyridine, &c., derivatives). The impartial way in which acetoacetic ester was found to behave, sometimes playing the part of a hydroxy-compottnd, sometimes that of a ketone, has led to much discussion on the merits of the formulre proposed by Geuther and Frankland, CIL.C(OH):CIJ.COOC2II5. CII:>CO.CHo.COOC2liri. Geuther's formula. Frankland's formula. From its physical properties and from its close analogy with compounds which are known in both dcsmotropic forms, there is now little doubt that the liquid is a mixture of both com- pounds, the proportion of each being determined by tempera- ture and other conditions. It is a typical example of 1automcr~ ism.1 PREPARATIONS 17—18. Monochloracetic Acid and Monobromacetic Acid. — The action of chlorine on the aliphatic acids takes place in presence of sunlight, also on the addition of small quantities of the " halogen-carriers," iodine, sulphur, and red phosphorus. By the action of iodine, I Cl is formed, which decomposes more readily than the molecule of chlorine, and hydriodic acid is liberated, CH8.COOH + IC1 = CHoCl.COOH + HI. The hydriodic acid is then decomposed by chlorine, and IC1 regenerated. Phosphorus acts by forming the chloride of phosphorus from which the acid chloride is produced, which is more readily attacked by chlorine than the acid. Sulphur behaves in a similar fashion, sulphur chloride converting the l For a full discussion of the subject of tautomer!sm, see the author's Organic Chemistry for Advanced Students, E. Arnold, London.